The following US Patents and patent applications are incorporated herein by reference:
U.S. Pat. No. 3,994,254 discloses a multiple-speed transmission for coupling an engine to the impeller of a marine jet drive, such that an overdrive connection powers the jet drive under operating conditions up to a predetermined upper limit of cruising speeds and such that a reduced drive, for example a direct-drive connection, is automatically established for jet-drive speeds in excess of the cruising conditions.
U.S. Pat. No. 4,173,939 discloses a marine propulsion device that incorporates a two-speed transmission including a first drive gear which is mounted for common rotation with an input shaft drivingly connected to an engine and which meshes with a first driven gear mounted for rotation coaxially with a drive shaft drivingly connected to the propeller shaft and further including a second drive gear which is mounted for rotation coaxially with and independently of the input shaft and which meshes with a second driven gear mounted for common rotation with the drive shaft.
U.S. Pat. No. 4,323,354 discloses a marine propulsion device that includes an input shaft drivingly connected to a power source, a lower unit having a rotatably mounted drive shaft extending in coaxial relation to the input shaft, and a propeller shaft rotatably mounted in the lower unit, the propeller shaft carrying a propeller. A two-speed transmission is provided to drivingly connect the input shaft to the drive shaft.
U.S. Pat. No. 4,331,432 discloses a marine propulsion device that includes an input shaft drivingly connected to a power source, a lower unit having a rotatably mounted drive shaft extending in coaxial relation to the input shaft, a rotatably mounted propeller shaft carrying a propeller and drivingly connected to the propeller shaft, and a two-speed transmission drivingly connecting the input shaft to the drive shaft.
U.S. Pat. No. 4,343,612 discloses an outboard motor that includes a power head having an engine, a propulsion leg extending downwardly from the power head, an input shaft housed in the propulsion leg and driven by the engine, a drive shaft housed in the propulsion leg, a propeller shaft in the propulsion leg and drivingly connected to the drive shaft, and a propeller mounted on the propeller shaft.
U.S. Pat. No. 5,494,466 discloses a transmission for a single engine drive for dual concentric propellers in a straight or V-drive arrangement with the straight-drive including four shafts and nine gears and the V-drive adding two more shafts and four more gears.
U.S. Pat. No. 7,891,263 discloses a shifting mechanism for an outboard drive of a watercraft. The shifting mechanism is located on a drive train generally aligned along a vertical axis and above a propulsion shaft of the lower unit. The drive train includes a rotatable input shaft which is driven by a motor.
U.S. Pat. No. 8,303,359 discloses an outboard motor that includes a transmission mechanism mounted between an output shaft of an engine and a propeller drive shaft. The transmission mechanism includes a clutch.
U.S. Patent Application Publication No. 2007/0125192 discloses a two speed transmission that includes an input shaft; a layshaft spaced from the input shaft; a first gear train connecting the input shaft to the layshaft; a second gear train connecting the layshaft to an output shaft the gear train including a one way clutch or similar; and a clutch for engaging the input shaft with the output shaft. The transmission is arranged such that when the output shaft is disengaged from the input shaft power is transmitted to the output shaft via the first and second gear trains and the layshaft.
U.S. Patent Application Publication No. 2014/0045393 discloses an outboard motor that is mounted on a stern of a boat and provided with a transmission and an oil pump. The transmission has a first-speed and second-speed gears, a first-speed gear clutch made of a mechanical dog clutch and a second-speed gear clutch made of a hydraulic clutch each adapted to engage the first and second-speed gears on a power transmission shaft, and a first-speed gear shift actuator adapted to couple the first-speed gear clutch with the first-speed gear. In the transmission, a first speed is established when the first-speed gear is engaged on the power transmission shaft and a second speed is established when the second-speed gear is engaged on the power transmission shaft while the first speed has been established such that power of the engine is transmitted to the propeller through the established speed.